This invention relates to injection devices, such as microneedle devices having an array of microneedles for placing on the skin.
Conventional methods of biological fluid sampling and non-oral drug delivery are normally invasive. That is, the skin is lanced to extract blood and measure various components when performing fluid sampling, or a drug delivery procedure is normally performed by injection, which causes pain and requires special medical training. Alternatives to drug delivery by injection have been disclosed, for example, by Henry, McAllister, Allen, and Prausnitz, of Georgia Institute of Technology (in a paper titled “Micromachined Needles for the Transdermal Delivery of Drugs”), U.S. Pat. No. 3,964,482, WO 98/00193, WO 97/48440, WO 97/48441, and WO 97/48442.
The use of microneedles has great advantages in that intracutaneous drug delivery can be accomplished without pain, leading to increased patient compliance, and without bleeding. Further, patients may apply the drug delivery devices themselves without extensive training. As used herein, the term “microneedles” refers to a plurality of elongated structures that are sufficiently long to penetrate through the stratum corneum skin layer and into the epidermal layer, yet are also sufficiently short to not penetrate to the dermal layer. However, if the dead cells have been completely or mostly removed from a portion of skin, then a very minute length of microneedle could be used to reach the viable epidermal tissue.
However, technical problems exist in the use of such microneedles. Among them is the plugging of hollow microneedles with skin or other tissues, thus, preventing the flow of therapeutic through the microneedle. This may have an impact on the amount of therapeutic actually delivered to the patient, which can be important for proper dosing.